adding dynamic text makes it move to earlier bars...

OK, this is really baffling me, there is not dynamic linked here, so that cannot be the issues. When I enter a text dynamic in one bar and hit enter, that dynamic appears 3 bars earlier instead.

see the after and before screenshots:

This happened in 2 places n the score now and the only way to get this fixed is by deleting all the dynamics in those bars and put them again, that seems to reset something.

The dynamics must be grouped, otherwise you would not be seeing that behaviour. Nevertheless, even when you have a dynamic group you should still be able to insert a dynamic in the middle of the group in the manner you tried, and that is something we will improve in future.